The tune itself IS an ancient tune. It was taken in 1856, by John(Iain in Gaelic) Cameron. The tune was Johnny Comes Lately to the Fair. He wrote a song called Chì Mi Na Mòrbheanna.

Later, the fellow you cited wrote his own song to the tune, which had been re-christened with that name.

For more on the song Ch&i Mi Na Mòbheanna, look it up at :

Ch&i Mi Na Mòbheanna

For the Hush, Hush/Smile ... There is a page on that someplace. Will have to look it up.